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We exist because of quantum mechanics, Messenger lecturer says

In physics, "things never just go haywire," said Nima Arkani-Hamed of Princeton University in his Oct. 5 Messenger Lecture. He argued that no new theories have come completely out of left field. Even with quantum mechanics, which revolutionized physics and philosophy in the early 20th century, "there was always a connection to pre-existing theory," he said.

Arkani-Hamed is a renowned Iranian-American physicist who studies high-energy physics, cosmology and string theory. His lecture, "Our Current Picture of the Universe -- and its Discontents," to a full house in Rockefeller Hall's Schwartz Auditorium was the second in his series of five Messenger Lectures this week on "The Future of Fundamental Physics."

In an hour and a half whirlwind, he summarized all the major advances in physics of the past 200 years. A common trend, he noted, is that new theories in physics have unified -- not separately explained -- the different phenomena we observe. For example, Newton's Laws tell us that the force pulling a falling apple to the ground is the same force that holds the moon in orbit around Earth; similarly, Maxwell's equations tell us that the force that creates lightening is the same force that holds a magnet to your refrigerator.

"Everything that's out there is an expression of less and less," he said.

However, physics keeps illuminating "more and more structure to emptiness," Arkani-Hamed said. Modern experiments have shown that even when you try to verify that a region of space is empty, particle/anti-particle pairs are produced out of the void. "Even the vacuum is exciting!" he exclaimed.

One hundred years ago, such basic questions about the world as "why is this table hard? Why is water wet?" were unanswerable, Arkani-Hamed said. Since the 1970s, however, with developments in quantum field theory, all known interactions have been described down to distances of 10-16 centimeters.

Physics today, he said, "leaves every question about the everyday world completely answered."

This framework of quantum field theory was dubbed the Standard Model of particle physics -- but he said it should have been called "the Super-Duper Awesomest Theory of All Time."

Arkani-Hamed is allured by particle physics, he said, because of "the fundamental beauty and simplicity of nature revealed at small distances."

He is also allured by physics at enormous distances -- specifically, with cosmological inflation. "The fact that the universe is expanding means that space is being invented all the time," he said.

It also means that the universe was once much smaller than it is today. He described the early universe as "a hot, dense soup of particles" colliding together, where it took hundreds of thousands of years for the "dense soup" to dilute enough for light to stream freely.

"This allowed the direct prediction that in every direction, we should see some remnant of photons from the big bang," he explained.

This prevalence of photons (known as cosmic background radiation), has indeed been observed everywhere in the universe. Fortunately for us, tiny quantum mechanical fluctuations in this background radiation "allowed gravity to take over, which is the origin of all structure," Arkani-Hamed said.

Particles clumped together, leading to the formation of stars, supernovae, planets and, eventually, us.

"Those inhomogeneities are where we come from," he said. "If inflation is correct, then you and I are here because of quantum mechanics."

The Messenger lectures are sponsored by the University Lectures Committee. The lectures were established in 1924 by a gift from Hiram Messenger, who graduated from Cornell in 1880.

Graduate student Melissa Rice is a writer intern at the Cornell Chronicle.

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